For some reason when I am using the editor in a template I've taken from your site, redesigned, and uploaded... every time I insert an image within the post, it resizes it so it's really small. I can't figure out why it's doing this.
Images are scaled down to whatever the width defined in your image tag is. So likely you have a small width defined in your template and the images are being scaled down to that width. You'll just want to edit your template code to reflect the larger image width.